Absorbent structures find application in absorbent articles particularly in the hygiene sector as for example in infant diapers, femcare products or incontinence products, and also in the wound covering and wound treatment sector, as for example in wound contact materials.
Absorbent structures comprising an assembly of successive plies of airlaid material are known.
Thus DE 10 2009 055 951 A1 shows an absorbent structure consisting of at least three plies—a liquid acquisition layer, a subsequent liquid storage layer comprising SAP, and a liquid distribution layer—where preferably all the layers consist of a airlaid material. Further examples of a ply sequence of airlaid materials of this kind are known from DE 10 2010 006 228 A1 and EP 1 191 915 B1.
A problem with which absorbent structures are oftentimes hampered, irrespective of their construction, is that the liquid collected therein, specifically body fluid with organic components, constitutes a nutrient medium for the growth of bacteria and other microorganisms. Frequent consequences include skin problems due to skin irritation, and also development of odors.
A known counter to this fundamental problem is the establishment of acidic pH levels in collections of fibers through addition of acidic, pH-controlling substances or of acidic fibers.
Thus EP 0 138 179 A2 shows the production of acidic fibers and the effect thereof in neutralizing a basic test serum.
EP 0 202 127 B1 discloses absorbent hygiene articles featuring an arrangement of separate plies of pH-controlling components and SAP.
EP 0 991 436 B1 shows absorbent articles whose absorbent element comprises pH-controlling substances in the form of a partially pH-neutralized SAP and fluff pulp with a pH of less than 7. When the article is wetted, the product pH levels out at between 3.5 and 4.9, with effects including a reduction in enzyme activities by microorganisms present.
Additionally known, from EP 2 086 596 B1, are absorbent articles of typical construction having an absorbent element, the absorbent element including acidic cellulose fibers having a pH below/equal to 5.5 and an organic zinc salt for suppressing or reducing production of ammonia. Similar content can be found in WO 2008/138386 A1, which shows absorbent articles having absorbent elements comprising acidic cellulose fibers or acidic SAP with a pH below/equal to 5.5 and an addition of benzoic acid, hydroxy benzoic acid or an ester.